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Fertilisers include many substances of organic or mineral origin, their
active constituents being :

Nitrogen, in the form of organic or insoluble nitrogen, as it occurs in dried
blood, meat guano, wool waste, horns, nails, leather, etc., bone meal, dung,
guano, excrements, etc. Nitric nitrogen, occurring mostly in sodium and
potassium nitrates. A mmoniacal nitrogen, in ammonium sulphate.

Potash, given especially by potassium nitrate, sulphate and chloride,
kainit, carnallite, etc.

Phosphoric acid, which may occur in the insoluble state (tricalcic phos-
phate), as in natural phosphates (phosphorites, apatites and coprolites),
bone ash, degelatinised bones, bone black, guano and other animal ferti-
lisers ; in a condition soluble in ammonium citrate (dicalcium phosphate),
as in precipitated phosphates and dephosphorisation slags ; in a condition
soluble in water (monocalcium phosphate), as in the superphosphates.

Analysis of fertilisers in general comprises essentially determinations of
the moisture, nitrogen, phosphoric acid (in its various forms) and potash.
These determinations are described among the general methods of analysis
(see p. 118). Other determinations to be made with special fertilisers are
given in the separate cases.

Of special importance in these analyses is the taking of the samples and
their preparation in the laboratory, the procedure to be followed being as
described below.

1. Taking and Despatch of Samples.óWith homogeneous powdered
fertilisers (phosphates, bone ash, sodium nitrate, ammonium sulphate, potash
fertilisers), several samples of 200-300 grams are taken either from various
points and different heights of the mass if this is in heaps, or from different
sacks. From these samples, which are more or less numerous according
to the magnitude of the parcel, a single heap (about 3-5 kilos) is made.
This is thoroughly mixed and any lumps broken to make it homogeneous,
the sample for analysis being then taken.

If the fertiliser is mixed, that is, prepared from powdered products mixed
according to definite formulae, a larger number of samples are taken and
mixed, portions from different parts of this being thoroughly mixed and
the sample for analysis taken from this heap.

With pasty fertilisers, a number of shovelfuls are taken and mixed well,
all lumps being broken down ; the sample for analysis is then taken.

With non-homogeneous and non-pulverulent fertilisers (bones, dried meat

117r the treatment with